In many types of reciprocating machines and particularly internal combustion engines, there may be time when it is desirable to change the valve operating characteristics during the running of the engine. Conventional variable valve timing mechanisms (VVT) have been proposed for varying the timing of opening and closing of the valves in an engine. By providing such variable valve timing it is possible to obtain improved engine performance over a wider range of engine speed and load conditions.
In addition to changing the valve timing events, there is also a desire to provide a mechanism that will change the lift of the valve. By changing the lift of the valve, the induction and/or exhaust efficiency of the engine can be changed during running to offer further enhancements in engine performance. Although the changing of the timing of the opening and closing of the valves utilizing a VVT mechanism is relatively easy to accomplish, the changing of the lift of the valve is more difficult to accomplish.
Because of the difficulty in changing the lift of the valve during the actual running of the engine, very complicated mechanisms have employed. Generally, one type of these mechanisms include follower devices that are interposed between the actuating camshaft and the valve and which change the degree of lift by changing the mechanical advantage between the cam and the actuated valve. Obviously, these systems become quite complicated. Furthermore, they frequently add to the reciprocating mass of the engine and can thus, deteriorate to some extent the engine performance.
In some instances, the variable lift is provided by substituting for the conventional type of cam and follower arrangement, an actual driving system which drives the valve without necessitating the use of a camshaft. These mechanisms become even more complicated than the variable follower mechanisms.
It is, therefore, a principal object of this invention to provide a variable lift valve-actuating mechanism for a reciprocating machine that easily permits the lift to be changed without significantly adding to the complexity of the actuating mechanism.
It is a further object of this invention to provide an improved camshaft arrangement for providing variable lift for the valve of a reciprocating machine.
It is a still further object of this invention to provide an improved engine camshaft for achieving variable valve lift in a relatively simple and inexpensive manner.